This invention relates to a process for preparing a polysilane by catalytic dehydrogenative condensation of an organo-trihydrosilane in the presence of an organotitanium or organozirconium complex catalyst. The present invention also pertains to a novel organozirconium complex catalyst.
Polysilanes are useful for application as an electrically conductive material, a luminescent material, a photoelectric conversion material, a nonlinear optical material, a photoresist material, a ceramic precursor, a polymerization initiator, etc.
One known process for the production of a polysilane includes subjecting an organo-trihydrosilane to dehydrogenative condensation in the presence of a ziroconocene silyl complex such as Cp2ZrMe2 (Organometallics, vol. 10, 3430-3432 (1991)). With this process, however, the weight average molecular weight of the polysilane is at most 5,000. To improve the polymerization degree, a method has been proposed in which a tri(perfluorophenyl)borane is added to the reaction system. Also known is a method in which hydrogen gas produced in situ is continuously removed from the reaction system. These methods, however, are not industrially advantageous. Furthermore, even with the above methods, the degree of polymerization is not high.
It is, therefore, an object of the present invention to provide a process which can produce a polysilane with a high degree of polymerization.
Another object of the present invention is to provide a zirconium complex catalyst which is useful for the production of a polysilane.
In accomplishing the above objects, there is provided in accordance with the present invention a zirconium complex represented by the following formula: 
wherein L1 represents a first group selected from the group consisting of (a) a dialkylaminoalkylcyclopentadienyl or branched alkylcyclopentadienyl group represented by the following formula (I): 
wherein R1 stands for an alkyl group having no more than 3 carbon atoms, X stands for N or CH and p represents an integer of 4 or less, (b) an xcex1-[(dialkylamino)alkyl]indenyl or branched alkylindenyl group represented by the following formula (II): 
wherein R2 stands for an alkyl group having no more than 3 carbon atoms, Y stands for N or CH and q represents an integer of 4 or less, and (c) a xcex2-[(dialkylamino)alkyl]indenyl or branched alkylindenyl group represented by the following formula (III): 
wherein R3 stands for an alkyl group having no more than 3 carbon atoms, Z stands for N or CH and m represents an integer of 4 or less, L2 represents a second group selected from the group consisting of (d) a cyclopentadienyl group represented by the formula (IV): 
and (e) a pentamethylcyclopentadienyl group represented by the formula (V): 
and L3 and L4 are each a monodendate anionic ligand.
In another aspect, the present invention provides a process for the production of a polysilane compound represented by the following formula (VII): 
wherein R4 represents an alkyl group having no more than 12 carbon atoms, an aryl group having no more than 12 carbon atoms, a cycloalkyl group having no more than 12 carbon atoms or an aralkyl group having no more than 12 carbon atoms and n is an integer of at least 8, said process comprising subjecting a trihydrosilane represented by the following formula (VI):
R4SiH3xe2x80x83xe2x80x83(VI)
wherein R4 is as defined above, to dehydrogenative condensation in the presence of a metal complex catalyst represented by the following formula (VIII): 
wherein M represents zirconium or titanium and L1, L2 L3 and L4 have the same meaning as above.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
In the process according to the present invention, an organotrihydrosilane of the above formula (VI) is subjected to catalytic dehydrogenative condensation. In the formula (VI), the alkyl group R4 may be, for example, phenyl, butyl, hexyl and xcex2-phenylethyl.
The catalyst is a zirconium or titanium complex of the above formula (VIII). In the formula (I), R1 is preferably methyl or ethyl and p is preferably 2 or 3. In the formula (II), R2 is preferably methyl or ethyl and q is preferably 2 or 3. In the formula (III), R3 is preferably methyl or ethyl and m is preferably 2 or 3. The catalyst is, used in a catalytically effective amount, generally 0.001 to 2 mol % based on the organotrihydrosilane of the formula (VI).
Each of the ligands represented by the formulas (I)-(V) is a cyclopentadienyl derivative. In the catalyst of the formula (VIII), L3 and L4 are preferably independently selected from the group consisting of an alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aralkyl group and a halogen group. If desired, a halogen-containing catalyst, i.e. a catalyst of the formula (VIII) in which L3 and L4 are halogen atoms, may be treated with a reducing agent, such as triethylaluminum, alumoxane, butyllithium or methyllithium, before or during the hydrogenative condensation of the trihydrosilane.
The catalytic dehydrogenative condensation may be carried out with or without using a solvent. The solvent, when used, may be, for example, a hydrocarbon such as benzene, toluene or hexane, or an ether such as diethyl ether, dibutyl ether or tetrahydrofuran. The reaction temperature is generally 0-150xc2x0 C., preferably from room temperature to 100xc2x0 C. Too high a temperature in excess of 150xc2x0 C. may cause the decomposition of the catalyst. A reaction temperature below 0xc2x0 C. requires a long reaction time and is economically disadvantageous. It is advisable to perform the reaction in an atmosphere of an inert gas such as nitrogen, argon or methane. The polysilane may be separated from the reaction mixture by any known method such as florisil chromatography.